Department of Biology

Program

Evolution, Ecology & Behavior

Research Areas

• Ecology
• Evolution
• Genomics and Bioinformatics

Education

B.S., 1990, Genetics, Cornell University
M.A., 1995, Philosophy of Science, Michigan State University
Ph.D., 1997, Genetics, Michigan State University

 

Research Description

Cooperation, conflict and multicellularity in the microbial world

Why live in groups rather than in isolation? Why cooperate with or cheat on your neighbor? How do the genetic foundations of social behavior evolve in real time? Under what conditions and by what mechanisms do cooperative behaviors originate or grow in complexity?

These and related questions about social behavior in higher fauna have long fascinated behavioral and evolutionary biologists. Recently, microbiologists have realized that group living - and the many questions that arise from it - also permeates the microbial world. Most microbial populations exist in a complex web of cooperative and competitive social interactions throughout their life in the soil, on surfaces or within a host. Microbiologists are only beginning to unravel the intricate nature of these social networks.

The social life of Myxobacteria

We pursue a wide range of questions about the ecology and evolution of social behavior in the Myxobacteria, which exhibit some of the most sophisticated cooperative behaviors in the bacterial kingdom. In particular, we focus on the model species Myxococcus xanthus, which engages in cooperative swarming, predation and multicellular development. Social swarming in M. xanthus requires cell-cell interactions and evolves rapidly in the lab and in the wild. Cooperative predation is accomplished by secretion of toxic and lytic compounds that immobilize and degrade prey organisms, thereby creating a public pool of growth substrates.    

Most dramatically, when M. xanthus runs low on amino acids (its primary nutrient source), individuals aggregate into high density groups (~100,000 cells), which then undergo genetically-based development into elevated fruiting bodies. This process requires several chemical social signals and only a portion of the cells within fruiting bodies differentiate into stress-resistant spores, while many others die. Some distinct genotypes are able to develop within the same fruiting body, thus generating a forum for genetic and behavioral conflict. We have shown that many different strains of M. xanthus cooperate as isolated clonal groups but antagonize and exploit one another in mixed populations.

We concentrate on M. xanthus and closely related Myxococcus species because thorough understanding of the evolutionary process requires fine-scale studies of adaptation and diversification. Toward this end, we perform evolution experiments in the lab, comparative studies of natural isolates and molecular/genomic analysis of lab-evolved and natural variation. Research themes of interest to our group include:

Experimental evolution in the lab
•  evolutionary degradation and restoration of cooperative behavior
•  cheating and anti-cheating behavioral strategies
•  predation performance
•  evolution of novel cooperation mechanisms
•  co-evolution

Behavior, ecology and evolution of natural strains
•  cooperation and conflict among strains during development, swarming and growth
•  Myxococcus xanthus local and global biogeography
•  natural variation in development, predation and motility
•  predatory specialization
•  functional roles of myxobacteria in soil community ecology

Genomics and molecular biology
•  complete sequencing of lab-evolved genomes to identify evolutionary mutations
•  molecular genetic analysis of evolutionary mutations in lab lines: fitness and phenotypic effects
•  evolution of genome-wide transcription patterns using DNA microarrays
•  genome-wide sequence variation among natural isolates
•  genetic and biochemical causes of social incompatibility among natural isolates

Select Publications

Voss, M. & G. Velicer. 2009.  Social Conflict in Centimeter-and Global-Scale Populations of the Bacterium Myxococcus xanthus.  Curr. Biol. 19(20): 1763-1767.

Vos, M. and G. J. Velicer. 2006. Genetic population structure of the soil bacterium Myxococcus xanthus at the centimeter scale. Applied & Environmental Microbiology 72, 3615-3625.

Velicer, G. J., G. Raddatz, H. Keller, S. Deiss, C. Lanz, I. Dinkelacker and S. C. Schuster. 2006. Comprehensive mutation identification in an evolved bacterial cooperator and its cheating ancestor. Proceedings of the National Academy of Sciences USA 103, 8107-8112.

Kadam, S. V. and G. J. Velicer. 2006. Variable patterns of density dependent survival in a social bacterium. Behavioral Ecology 17, 833-838.

Fiegna, F., Y.-T. N. Yu, S. V. Kadam and G. J. Velicer. 2006. Evolution of an obligate social cheater to a superior cooperator. Nature, 441, 310-314.

Fiegna, F. and G. J. Velicer. 2005. Exploitative and hierarchical antagonism in a cooperative bacterium. PLoS Biology, 3, 1980-1987.

Hillesland, K. L. and G. J. Velicer. 2005. Resource level affects relative performance of the two Myxococcus xanthus motility systems. Microbial Ecology, 49, 558-66 .

Travisano, M. and G. J. Velicer. 2004. Strategies of microbial cheater control. Trends in Microbiology, 12, 72-78.

Velicer, G. J. and Y. N. Yu. 2003. Evolution of novel cooperative swarming in the bacterium Myxococcus xanthus.   Nature, 425, 75-78.

Velicer, G. J., L. Kroos, and R. E. Lenski. 2000. Developmental cheating in the social bacterium Myxococcus xanthus. Nature, 404, 598-601.

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